Hard drive making a strange noise

I just bought 2 250 gig western digital hard drivesa and hooked them up externally. After I filled up the first one it started making strange sounds when accessing files. Kind of like a low intermident grumbling sound or sometimes longer grumbling sounds when searching for files. It’s too loud but it is noticable
I took it back to the shop to check it out and they just gave me another one. now the second and new drive is doing the same thing but slightly different sounds.
I have lots of small files on each disk. Could that be the reason or could it be a bad batch of drives. I got them at a little stand in the computer market. 'm really worried about losing my data so I got a third drive to back them up it’s really expensive to have to buy twice as many gigs as I need.

Clicking drives would worry me, too.

Are you sure they’re genuine?

Kenneth

Some hard drives do make more noise than others, but for piece of mind, I recommend taking it back and getting another (maybe even another brand). Tell them you are not happy with it making those noises and you will keep taking it back till they give you a quiet one.

My PC at work sometimes makes clunking noises, but they usually subside after I cease kicking the box.

Go figure.